Hair spray and bellows: what they have in common

1. Step 1. Hair spray — uses — Aerosol can. Hair spray comes out of an aerosol can as fine droplets, so it settles as an even film.
2. Step 2. Aerosol can — has part — Valve. A valve.
3. Step 3. Valve — is part of — Bellows. A valve in the bellows lets air in when they open and keeps it from escaping back.

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